The focusing and aiming of free-space beams onto a target is critical in such applications as fiber optics. It is often necessary to provide a long-range of travel for the focused beam while maintaining a small, undistorted spot and maintaining the average incidence angle within the angular tolerance of the target. Attempted solutions have failed to achieve all these objectives or do so in a manner that is inefficient or unwieldy.
For example, single lens launchers do not provide enough degrees of freedom to compensate for common fabrication errors. For instance, if the incoming beam is not centered on the target to begin with, all the light may not enter the target no matter how well the lens is adjusted in a single lens launcher. Two-lens launchers provide more degrees of freedom, but the angle cannot be adjusted independent of the position. The apparatus disclosed in U.S. Pat. No. 5,077,622, titled "Apparatus For Precision Focussing and Positioning of A Beam Waist On A Target" and issued Dec. 31, 1991 to Lynch et al, achieves high-resolution positioning, but requires at least seven separate adjustment axes and is difficult to fit in a compact package. Finally, tapered fibers reduce the resolution required by making the target bigger at the input and tapering down to the final size. In addition to being expensive, these are also less efficient since light is lost in the taper. Indeed, the larger the taper the more light is lost. Tapered fibers are also not useful for polarization-maintaining applications, since the taper scrambles the polarization of the light.